Security devices

ABSTRACT

A combination comprising a document having an image applied thereto and a security device affixed to a surface of the document. The security device comprising a first layer applied on the image. The first layer comprising a first and a second portion in communication with a first and second image area of the image, respectively. The first layer comprising a coating composition comprising fully exfoliated single sheets of graphene. The first portion comprises: a first detectable property having a first value correlated with the fully exfoliated single sheets of graphene; a first X-ray diffraction pattern; and a first electrical conductivity. The second portion comprises a second detectable property comprising: a second value correlated with the fully exfoliated single sheets of graphene; a second X-ray diffraction pattern; and a second electrical conductivity. The first and second detectable properties are not equal and together create a distinctive signature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior application Ser. No.15/610,790, filed Jun. 1, 2017; and claims priority to U.S. provisionalapplication No. 61/413,968, filed on Nov. 15, 2010. The entire contentsof both applications are hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to security devices prepared by coating animaged substrate with a composition comprising graphene sheets.

BACKGROUND

The protection of a wide range of material goods and documents fromtampering, fraud, counterfeiting, theft, etc. is of rapidly growingconcern. Counterfeit products, for example, can not only lead to lostrevenues for the producers of the genuine goods, but can also causesignificant health and safety risks. Counterfeit pharmaceuticals, forexample, can be difficult to detect without the right authenticationmethods. Furthermore, there is a need to be able to effectively trackgoods as they are transported and used. Many solutions for theseproblems use expensive or elaborate solutions, many of which are “overt”(i.e. the presence of the security feature is clearly visible to theobserver). It would be desirable to obtain a security device that canhave multiple levels of security, can be simple and inexpensive to makeand operate, and that can be covert (i.e., an uninitiated viewer willnot necessarily know that it is present).

SUMMARY OF THE INVENTION

Disclosed and claimed herein is a multilayered security device,comprising a first layer comprising a patterned substrate and a secondlayer overlying the pattern, comprising a coating composition comprisinggraphene sheets. Also disclosed and claimed is a method of making amultilayered security device, comprising applying a coating compositioncomprising graphene sheets to a patterned substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a shows a patterned substrate.

FIG. 1b shows a security device comprising a patterned substrate coatedwith a graphene-based coating composition.

FIG. 2a shows a patterned substrate where the pattern contains lighterand darker regions.

FIG. 2b shows a security device comprising a patterned substrate wherethe pattern contains lighter and darker regions that has been coatedwith a graphene-based coating composition.

DETAILED DESCRIPTION OF THE INVENTION

The security device of the application comprises a multilayered articlecomprising an substrate that has been imaged with a pattern (referred toherein as the “image”) over which is applied a coating compositioncomprising graphene sheets to give a coated surface. The portions of thecoated surface over the pattern have different properties from theportions of the coated surface over un-imaged portions of the substrate(referred to as “background areas”). The imaged substrate may or may nothave any background areas. The substrate may also be imaged in such away that portions of the coated surface have different properties overdifferent parts of the pattern. The properties may include one or moreof electrical or thermal conductivity, optical properties (such asoptical density, color coordinates, etc.), X-ray diffraction (XRD)pattern, etc.

The security device may be used to hide or disguise unique patterns andcodes that can only be read, and in some cases, detected, by followingspecific methods.

For example, FIG. 1a shows a patterned substrate 10 that has been imagedwith a pattern 11, leaving a background area 15. FIG. 1b shows asecurity device 13 made by coating the patterned substrate 10 with acoating 12, which also covers pattern 11. The portion 14 of the coatingthat covers the image 11 has different properties from the portion ofthe coating that lies over the background area 15.

FIG. 2a shows a patterned substrate 20 that has been imaged with apattern containing a lighter portion 21 and a darker portion 22. FIG. 2bshows a security device 23 made by coating the patterned substrate 20with a coating 24 that also covers portions 21 and 22 of the pattern.The areas of the coating covering portions 21 and 22 may have differentproperties from each other and from the portions of the coating coveringthe background area.

Some or all of the image may be visible through the coating. In anotherembodiment, at least a portion or all of the image may be difficult ornot possible to detect visually through the coating. The opacity, colorcoordinates, and other optical properties of the coating and/or thepattern may be adjusted to achieve a desired degree of visibility of thepattern through the coating.

The coated image may have a different properties from the backgroundarea and different portions of the coated image may have differentproperties from each other.

The coating composition comprises graphene sheets, and, optionally, atleast one binder, at least one carrier, one or more functional additivesto adjust the optical properties, conductivity, XRD pattern, or otherproperties of the coating, and/or one or more additional additives.Functional additives can include electrochromic and photochromicpigments.

There are no particular limitations to the form taken by the substrate.Substrates include, but are not limited to, flexible and/or stretchablematerials, silicones and other elastomers and other polymeric materials,metals (such as aluminum, copper, steel, stainless steel, etc.),adhesives, fabrics (including cloths) and textiles (such as cotton,wool, polyesters, rayon, etc.), clothing, glasses and other minerals,ceramics, silicon surfaces, wood, paper, cardboard, paperboard,cellulose-based materials, glassine, labels, silicon and othersemiconductors, laminates, corrugated materials, concrete, bricks, andother building materials, etc. Substrates may in the form of films,papers, wafers, larger three-dimensional objects, etc.

The substrates may have been treated with other materials before theimages are applied. Examples include substrates (such as PET) coatedwith indium tin oxide, antimony tin oxide, etc. They may be woven,nonwoven, in mesh form; etc.

The substrates may be paper-based materials generally (including paper,paperboard, cardboard, glassine, etc.). Paper-based materials can besurface treated. Examples of surface treatments include coatings such aspolymeric coatings, which can include PET, polyethylene, polypropylene,acetates, nitrocellulose, etc. Coatings may be adhesives. The paperbased materials may be of sized.

Examples of polymeric materials include, but are not limited to, thosecomprising thermoplastics and thermosets, including elastomers andrubbers (including thermoplastics and thermosets), silicones,fluorinated polysiloxanes, natural rubber, butyl rubber,chlorosulfonated polyethylene, chlorinated polyethylene,styrene/butadiene copolymers (SBR), styrene/ethylene/butadiene/stryenecopolymers (SEBS), styrene/ethylene/butadiene/stryene copolymers graftedwith maleic anhydride, styrene/isoprene/styrene copolymers (SIS),polyisoprene, nitrile rubbers, hydrogenated nitrile rubbers, neoprene,ethylene/propylene copolymers (EPR), ethylene/propylene/diene copolymers(EPDM), ethylene/vinyl acetate copolymer (EVA),hexafluoropropylene/vinylidene fluoride/tetrafluoroethylene copolymers,tetrafluoroethylene/propylene copolymers, fluorelastomers, polyesters(such as poly(ethylene terephthalate), poly(butylene terephthalate),poly(ethylene naphthalate), liquid crystalline polyesters, poly(lacticacid), etc.); polystyrene; polyamides (including polyterephthalamides);polyimides (such as Kapton®); aramids (such as Kevlar® and Nomex®);fluoropolymers (such as fluorinated ethylene propylene (FEP),polytetrafluoroethylene (PTFE), poly(vinyl fluoride), poly(vinylidenefluoride), etc.); polyetherimides; poly(vinyl chloride); poly(vinylidenechloride); polyurethanes (such as thermoplastic polyurethanes (TPU);spandex, cellulosic polymers (such as nitrocellulose, cellulose acetate,etc.); styrene/acrylonitriles polymers (SAN);arcrylonitrile/butadiene/styrene polymers (ABS); polycarbonates;polyacrylates; poly(methyl methacrylate); ethylene/vinyl acetatecopolymers; thermoset epoxies and polyurethanes; polyolefins (such aspolyethylene (including low density polyethylene, high densitypolyethylene, ultrahigh molecular weight polyethylene, etc.),polypropylene (such as biaxially-oriented polypropylene, etc.); Mylar;etc. They may be non-woven materials, such as DuPont Tyvek®. They may beadhesive or adhesive-backed materials (such as adhesive-backed papers orpaper substitutes). They may be mineral-based paper substitutes such asTeslin® from PPG Industries. The substrate may be a transparent ortranslucent or optical material, such as glass, quartz, polymer (such aspolycarbonate or poly(meth)acrylates (such as poly(methyl methacrylate).

Substrates may be packaging material, currency, financial instruments,etc.

The pattern may be applied to the substrate using any suitable method,including, but not limited to, painting, coating, printing, pouring,spin casting, solution casting, dip coating, powder coating, by syringeor pipette, spray coating, curtain coating, lamination, co-extrusion,electrospray deposition, ink-jet printing, spin coating, thermaltransfer (including laser transfer) methods, doctor blade printing, wirerod printing, screen printing, rotary screen printing, gravure printing,lithographic printing, intaglio printing, digital printing, capillaryprinting, offset printing, microprinting, electrohydrodynamic (EHD)printing (a method of which is described in WO 2007/053621, which ishereby incorporated herein by reference), flexographic printing, padprinting, stamping, tampon printing, xerography, microcontact printing,dip pen nanolithography, laser printing, drawing, writing, coloring, viapen, or similar means, etc.

The pattern may be made from any suitable medium including, but notlimited to, paints, inks, varnishes, toners and other solid orpowder-based printing media, inkjet inks, water-based inks and coatings,solvent based inks and coatings, pencils and pens, chalk and otherminerals, crayons, etc. The media may use carbon-based dyes and/orpigments, colored dyes and/or pigments, coatings that arepigment/dye-free, etc.

The pattern may take on any form. It may be in the form of shapes,lines, characters (such as letters, numbers, symbols, etc.), lines, barcodes (including two-dimensional and three-dimensional bar codes, etc.),arbitrary designs and patterns, etc. The pattern can have a uniform ornon-uniform thickness.

The presence of the underlying pattern may be detected by a user usingmethods such as measuring electrical and/or thermal conductivity,optical density, color coordinates, XRD patterns, etc. A variety ofdevices, including handheld, wireless, etc. devices may be used. Anysuitable color coordinates system (such as Lab) may be used.

In some embodiments, if the pattern is formed using different densitiesand/or thicknesses of a coating, ink, toner, etc. in different areas ofthe pattern, the coated surface can have different properties. If thepattern is formed using different coatings, inks, toners, etc. indifferent areas of the pattern, the coated surface can have differentproperties in those areas. The variable properties in different portionsof the pattern can be used to create a distinctive signature in thesecurity device and provide an additional layer of security.

The graphene sheets are graphite sheets preferably having a surface areaof from about 100 to about 2630 m²/g. In some embodiments, the graphenesheets primarily, almost completely, or completely comprise fullyexfoliated single sheets of graphite (these are approximately 1 nm thickand are often referred to as “graphene”), while in other embodiments, atleast a portion of the graphene sheets may comprise at partiallyexfoliated graphite sheets, in which two or more sheets of graphite havenot been exfoliated from each other. The graphene sheets may comprisemixtures of fully and partially exfoliated graphite sheets.

Graphene sheets may be made using any suitable method. For example, theymay be obtained from graphite, graphite oxide, expandable graphite,expanded graphite, etc. They may be obtained by the physical exfoliationof graphite, by for example, peeling off sheets graphene sheets. Theymay be made from inorganic precursors, such as silicon carbide. They maybe made by chemical vapor deposition (such as by reacting a methane andhydrogen on a metal surface). They may be made by the reduction of analcohol, such ethanol, with a metal (such as an alkali metal likesodium) and the subsequent pyrolysis of the alkoxide product (such amethod is reported in Nature Nanotechnology (2009), 4, 30-33). They maybe made by the exfoliation of graphite in dispersions or exfoliation ofgraphite oxide in dispersions and the subsequently reducing theexfoliated graphite oxide. Graphene sheets may be made by theexfoliation of expandable graphite, followed by intercalation, andultrasonication or other means of separating the intercalated sheets(see, for example, Nature Nanotechnology (2008), 3, 538-542). They maybe made by the intercalation of graphite and the subsequent exfoliationof the product in suspension, thermally, etc.

Graphene sheets may be made from graphite oxide (also known as graphiticacid or graphene oxide). Graphite may be treated with oxidizing and/orintercalating agents and exfoliated. Graphite may also be treated withintercalating agents and electrochemically oxidized and exfoliated.Graphene sheets may be formed by ultrasonically exfoliating suspensionsof graphite and/or graphite oxide in a liquid (which may containsurfactants and/or intercalants). Exfoliated graphite oxide dispersionsor suspensions can be subsequently reduced to graphene sheets. Graphenesheets may also be formed by mechanical treatment (such as grinding ormilling) to exfoliate graphite or graphite oxide (which wouldsubsequently be reduced to graphene sheets).

Reduction of graphite oxide to graphene may be by means of chemicalreduction and may be carried out in graphite oxide in a solid form, in adispersion, etc. Examples of useful chemical reducing agents include,but are not limited to, hydrazines (such as hydrazine,N,N-dimethylhydrazine, etc.), sodium borohydride, citric acid,hydroquinone, isocyanates (such as phenyl isocyanate), hydrogen,hydrogen plasma, etc. A dispersion or suspension of exfoliated graphiteoxide in a carrier (such as water, organic solvents, or a mixture ofsolvents) can be made using any suitable method (such as ultrasonicationand/or mechanical grinding or milling) and reduced to graphene sheets.

Graphite oxide may be produced by any method known in the art, such asby a process that involves oxidation of graphite using one or morechemical oxidizing agents and, optionally, intercalating agents such assulfuric acid. Examples of oxidizing agents include nitric acid, sodiumand potassium nitrates, perchlorates, hydrogen peroxide, sodium andpotassium permanganates, phosphorus pentoxide, bisulfites, etc.Preferred oxidants include KClO₄; HNO₃ and KClO₃; KMnO₄ and/or NaMnO₄;KMnO₄ and NaNO₃; K₂S₂O₈ and P₂O₅ and KMnO₄; KMnO₄ and HNO₃; and HNO₃.Preferred intercalation agents include sulfuric acid. Graphite may alsobe treated with intercalating agents and electrochemically oxidized.Examples of methods of making graphite oxide include those described byStaudenmaier (Ber. Stsch. Chem. Ges. (1898), 31, 1481) and Hummers (J.Am. Chem. Soc. (1958), 80, 1339).

One example of a method for the preparation of graphene sheets is tooxidize graphite to graphite oxide, which is then thermally exfoliatedto form graphene sheets (also known as thermally exfoliated graphiteoxide), as described in US patent application publication 2007/0092432,the disclosure of which is incorporated herein by reference. The thuslyformed graphene sheets may display little or no signature correspondingto graphite or graphite oxide in their X-ray diffraction pattern.

The thermal exfoliation may be carried out in a continuous,semi-continuous batch, etc. process.

Heating can be done in a batch process or a continuous process and canbe done under a variety of atmospheres, including inert and reducingatmospheres (such as nitrogen, argon, and/or hydrogen atmospheres).Heating times can range from under a few seconds or several hours ormore, depending on the temperatures used and the characteristics desiredin the final thermally exfoliated graphite oxide. Heating can be done inany appropriate vessel, such as a fused silica, mineral, metal, carbon(such as graphite), ceramic, etc. vessel. Heating may be done using aflash lamp.

During heating, the graphite oxide may be contained in an essentiallyconstant location in single batch reaction vessel, or may be transportedthrough one or more vessels during the reaction in a continuous or batchmode. Heating may be done using any suitable means, including the use offurnaces and infrared heaters.

Examples of temperatures at which the thermal exfoliation of graphiteoxide may be carried out are at least about 300° C., at least about 400°C., at least about 450° C., at least about 500° C., at least about 600°C., at least about 700° C., at least about 750° C., at least about 800°C., at least about 850° C., at least about 900° C., at least about 950°C., and at least about 1000° C. Preferred ranges include between about750 and about 3000° C., between about 850 and about 2500° C., betweenabout 950 and about 2500° C., and between about 950 and about 1500° C.

The time of heating can range from less than a second to many minutes.For example, the time of heating can be less than about 0.5 seconds,less than about 1 second, less than about 5 seconds, less than about 10seconds, less than about 20 seconds, less than about 30 seconds, or lessthan about 1 min. The time of heating can be at least about 1 minute, atleast about 2 minutes, at least about 5 minutes, at least about 15minutes, at least about 30 minutes, at least about 45 minutes, at leastabout 60 minutes, at least about 90 minutes, at least about 120 minutes,at least about 150 minutes, at least about 240 minutes, from about 0.01seconds to about 240 minutes, from about 0.5 seconds to about 240minutes, from about 1 second to about 240 minutes, from about 1 minuteto about 240 minutes, from about 0.01 seconds to about 60 minutes, fromabout 0.5 seconds to about 60 minutes, from about 1 second to about 60minutes, from about 1 minute to about 60 minutes, from about 0.01seconds to about 10 minutes, from about 0.5 seconds to about 10 minutes,from about 1 second to about 10 minutes, from about 1 minute to about 10minutes, from about 0.01 seconds to about 1 minute, from about 0.5seconds to about 1 minute, from about 1 second to about 1 minute, nomore than about 600 minutes, no more than about 450 minutes, no morethan about 300 minutes, no more than about 180 minutes, no more thanabout 120 minutes, no more than about 90 minutes, no more than about 60minutes, no more than about 30 minutes, no more than about 15 minutes,no more than about 10 minutes, no more than about 5 minutes, no morethan about 1 minute, no more than about 30 seconds, no more than about10 seconds, or no more than about 1 second. During the course ofheating, the temperature may vary.

Examples of the rate of heating include at least about 120° C./min, atleast about 200° C./min, at least about 300° C./min, at least about 400°C./min, at least about 600° C./min, at least about 800° C./min, at leastabout 1000° C./min, at least about 1200° C./min, at least about 1500°C./min, at least about 1800° C./min, and at least about 2000° C./min.

Graphene sheets may be annealed or reduced to graphene sheets havinghigher carbon to oxygen ratios by heating under reducing atmosphericconditions (e.g., in systems purged with inert gases or hydrogen).Reduction/annealing temperatures are preferably at least about 300° C.,or at least about 350° C., or at least about 400° C., or at least about500° C., or at least about 600° C., or at least about 750° C., or atleast about 850° C., or at least about 950° C., or at least about 1000°C. The temperature used may be, for example, between about 750 and about3000° C., or between about 850 and about 2500° C., or between about 950and about 2500° C.

The time of heating can be for example, at least about 1 second, or atleast about 10 seconds, or at least about 1 minute, or at least about 2minutes, or at least about 5 minutes. In some embodiments, the heatingtime will be at least about 15 minutes, or about 30 minutes, or about 45minutes, or about 60 minutes, or about 90 minutes, or about 120 minutes,or about 150 minutes. During the course of annealing/reduction, thetemperature may vary within these ranges.

The heating may be done under a variety of conditions, including in aninert atmosphere (such as argon or nitrogen) or a reducing atmosphere,such as hydrogen (including hydrogen diluted in an inert gas such asargon or nitrogen), or under vacuum. The heating may be done in anyappropriate vessel, such as a fused silica or a mineral or ceramicvessel or a metal vessel. The materials being heated including anystarting materials and any products or intermediates) may be containedin an essentially constant location in single batch reaction vessel, ormay be transported through one or more vessels during the reaction in acontinuous or batch reaction. Heating may be done using any suitablemeans, including the use of furnaces and infrared heaters.

The graphene sheets preferably have a surface area of at least about 100m²/g to, or of at least about 200 m²/g, or of at least about 300 m²/g,or of at least about 350 m²/g, or of at least about 400 m²/g, or of atleast about 500 m²/g, or of at least about 600 m²/g, or of at leastabout 700 m²/g, or of at least about 800 m²/g, or of at least about 900m²/g, or of at least about 700 m²/g. The surface area may be about 400to about 1100 m²/g. The theoretical maximum surface area can becalculated to be 2630 m²/g. The surface area includes all values andsubvalues therebetween, especially including 400, 500, 600, 700, 800,900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000,2100, 2200, 2300, 2400, 2500, and 2630 m²/g.

The graphene sheets can have number average aspect ratios of about 100to about 100,000, or of about 100 to about 50,000, or of about 100 toabout 25,000, or of about 100 to about 10,000 (where “aspect ratio” isdefined as the ratio of the longest dimension of the sheet to theshortest).

Surface area can be measured using either the nitrogen adsorption/BETmethod at 77 K or a methylene blue (MB) dye method in liquid solution.

The dye method is carried out as follows: A known amount of graphenesheets is added to a flask. At least 1.5 g of MB are then added to theflask per gram of graphene sheets. Ethanol is added to the flask and themixture is ultrasonicated for about fifteen minutes. The ethanol is thenevaporated and a known quantity of water is added to the flask tore-dissolve the free MB. The undissolved material is allowed to settle,preferably by centrifuging the sample. The concentration of MB insolution is determined using a UV-vis spectrophotometer by measuring theabsorption at λ_(max)=298 nm relative to that of standardconcentrations.

The difference between the amount of MB that was initially added and theamount present in solution as determined by UV-vis spectrophotometry isassumed to be the amount of MB that has been adsorbed onto the surfaceof the graphene sheets. The surface area of the graphene sheets are thencalculated using a value of 2.54 m² of surface covered per one mg of MBadsorbed.

The graphene sheets may have a bulk density of from about 0.1 to atleast about 200 kg/m³. The bulk density includes all values andsubvalues therebetween, especially including 0.5, 1, 5, 10, 15, 20, 25,30, 35, 50, 75, 100, 125, 150, and 175 kg/m³.

The graphene sheets may be functionalized with, for example,oxygen-containing functional groups (including, for example, hydroxyl,carboxyl, and epoxy groups) and typically have an overall carbon tooxygen molar ratio (C/O ratio), as determined by elemental analysis ofat least about 1:1, or more preferably, at least about 3:2. Examples ofcarbon to oxygen ratios include about 3:2 to about 85:15; about 3:2 toabout 20:1; about 3:2 to about 30:1; about 3:2 to about 40:1; about 3:2to about 60:1; about 3:2 to about 80:1; about 3:2 to about 100:1; about3:2 to about 200:1; about 3:2 to about 500:1; about 3:2 to about 1000:1;about 3:2 to greater than 1000:1; about 10:1 to about 30:1; about 80:1to about 100:1; about 20:1 to about 100:1; about 20:1 to about 500:1;about 20:1 to about 1000:1; about 50:1 to about 300:1; about 50:1 toabout 500:1; and about 50:1 to about 1000:1. In some embodiments, thecarbon to oxygen ratio is at least about 10:1, or at least about 20:1,or at least about 35:1, or at least about 50:1, or at least about 75:1,or at least about 100:1, or at least about 200:1, or at least about300:1, or at least about 400:1, or at least 500:1, or at least about750:1, or at least about 1000:1; or at least about 1500:1, or at leastabout 2000:1. The carbon to oxygen ratio also includes all values andsubvalues between these ranges.

The graphene sheets may contain atomic scale kinks. These kinks may becaused by the presence of lattice defects in, or by chemicalfunctionalization of the two-dimensional hexagonal lattice structure ofthe graphite basal plane.

The coating compositions may further comprise graphite (includingnatural, Kish, and synthetic, annealed, pyrolytic, highly orientedpyrolytic, etc. graphites) and/or graphite oxide. The ratio by weight ofgraphite and/or graphite oxide to graphene sheets may be from about 2:98to about 98:2, or from about 5:95 to about 95:5, or from about 10:90 toabout 90:10, or from about 20:80 to about 80:20, or from about 30:70 to70:30, or from about 40:60 to about 90:10, or from about 50:50 to about85:15, or from about 60:40 to about 85:15, or from about 70:30 to about85:15.

The amounts of graphene sheets having different C/O ratios, graphite,graphite oxide and/or other additives can be adjusted to obtain acoating having desired properties.

The graphene sheets may comprise two or more graphene powders havingdifferent particle size distributions and/or morphologies. The graphitemay also comprise two or more graphite powders having different particlesize distributions and/or morphologies.

When used, binders can be thermoplastics or thermosets and may beelastomers. Binders may also comprise monomers that can be polymerizedbefore, during, or after the application of the coating to thesubstrate. Polymeric binders may be crosslinked or otherwise cured afterthe coating has been applied to the substrate. Examples of polymericbinders include polysiloxanes (such as poly(dimethylsiloxane),dimethylsiloxane/vinylmethylsiloxane copolymers, vinyldimethylsiloxaneterminated poly(dimethylsiloxane), etc.), polyethers and glycols such aspoly(ethylene oxide)s (also known as poly(ethylene glycol)s,poly(propylene oxide)s (also known as poly(propylene glycol)s, andethylene oxide/propylene oxide copolymers, cellulosic resins (such asethyl cellulose, ethyl hydroxyethyl cellulose, carboxymethyl cellulose,cellulose acetate, cellulose acetate propionates, and cellulose acetatebutyrates), and poly(vinyl butyral), polyvinyl alcohol and itsderivatives, ethylene/vinyl acetate polymers, acrylic polymers andcopolymers (such as methyl methacrylate polymers, methacrylatecopolymers, polymers derived from one or more acrylates, methacrylates,ethyl acrylates, ethyl methacrylates, butyl acrylates, butylmethacrylates and the like), styrene/acrylic copolymers, styrene/maleicanhydride copolymers, isobutylene/maleic anhydride copolymers, vinylacetate/ethylene copolymers, ethylene/acrylic acid copolymers,polyolefins, polystyrenes, olefin and styrene copolymers, epoxy resins,acrylic latex polymers, polyester acrylate oligomers and polymers,polyester diol diacrylate polymers, UV-curable resins, and polyamides.Polyamides may be polymers and copolymers (i.e., polyamides having atleast two different repeat units) having melting points between about100 and about 255° C., or between about 120 and about 255° C., orbetween about 110 and about 255° C. or between about 120 and about 255°C. These include aliphatic copolyamides having a melting point of about230° C. or less, aliphatic copolyamides having a melting point of about210° C. or less, aliphatic copolyamides having a melting point of about200° C. or less, aliphatic copolyamides having a melting point of about180° C. or less, of about 150° C. or less, of about 130° C. or less, ofabout 120° C. or less, of about 110° C. or less, etc. Examples of theseinclude those sold under the trade names Macromelt by Henkel, Versamidby Cognis, and Elvamide® by DuPont. Examples of suitable polymersinclude Elvacite® polymers supplied by Lucite International, Inc.,including Elvacite® 2009, 2010, 2013, 2014, 2016, 2028, 2042, 2045,2046, 2550, 2552, 2614, 2669, 2697, 2776, 2823, 2895, 2927, 3001, 3003,3004, 4018, 4021, 4026, 4028, 4044, 4059, 4400, 4075, 4060, 4102, etc.Other polymer families include Bynel® polymers (such as Bynel® 2022supplied by DuPont) and Joncryl® polymers (such as Joncryl® 678 and682).

The coating compositions optionally comprise one or more carriers inwhich some or all of the components are dissolved, suspended, orotherwise dispersed or carried. Examples of suitable carriers include,but are not limited to, water, distilled or synthetic isoparaffinichydrocarbons (such Isopar® and Norpar® (both manufactured by Exxon) andDowanol® (manufactured by Dow), citrus terpenes and mixtures containingcitrus terpenes (such as Purogen, Electron, and Positron (allmanufactured by Ecolink)), terpenes and terpene alcohols (includingterpineols, including alpha-terpineol), limonene, aliphatic petroleumdistillates, alcohols (such as methanol, ethanol, n-propanol,i-propanol, n-butanol, i-butanol, sec-butanol, tert-butanol, pentanols,i-amyl alcohol, hexanols, heptanols, octanols, diacetone alcohol, butylglycol, etc.), ketones (such as acetone, methyl ethyl ketone,cyclohexanone, i-butyl ketone, 2,6,8,trimethyl-4-nonanone etc.), esters(such as methyl acetate, ethyl acetate, n-propyl acetate, i-propylacetate, n-butyl acetate, i-butyl acetate, tert-butyl acetate, carbitolacetate, etc.), glycol ethers, ester and alcohols (such as2-(2-ethoxyethoxy)ethanol, propylene glycol monomethyl ether and otherpropylene glycol ethers; ethylene glycol monobutyl ether, 2-methoxyethylether (diglyme), propylene glycol methyl ether (PGME); and otherethylene glycol ethers; ethylene and propylene glycol ether acetates,diethylene glycol monoethyl ether acetate, 1-methoxy-2-propanol acetate(PGMEA); and hexylene glycol (such as Hexasol™ (supplied bySpecialChem)), imides, amides (such as dimethyl formamide,dimethylacetamide, etc.), cyclic amides (such as N-methylpyrrolidone and2-pyrrolidone), lactones (such as beta-propiolactone,gamma-valerolactone, delta-valerolactone, gamma-butyrolactone,epsilon-caprolactone), cyclic imides (such as imidazolidinones such asN,N′-dimethylimidazolidinone (1,3-dimethyl-2-imidazolidinone)), andmixtures of two or more of the foregoing and mixtures of one or more ofthe foregoing with other carriers. Solvents may be low- or non-VOCsolvents, non-hazardous air pollution solvents, and non-halogenatedsolvents.

The graphene sheets and graphite, if present, are preferably present inthe compositions in about 20 to about 98 weight percent, in about 30 toabout 95 weight percent, in about 40 to about 95 weight percent, inabout 50 to about 95 weight percent, and in about 70 to about 95 weightpercent, based on the total amount of graphene sheets and graphite, ifpresent, and binder.

The compositions may be made using any suitable method, including wet ordry methods and batch, semi-continuous, and continuous methods.

For example, components of the coating compositions, such as one or moreof the graphene sheets, graphite (if used), binders, carriers, and/orother components may be processed (e.g., milled/ground, blended, etc. byusing suitable mixing, dispersing, and/or compounding techniques andapparatus, including ultrasonic devices, high-shear mixers, ball mills,attrition equipment, sandmills, two-roll mills, three-roll mills,cryogenic grinding crushers, extruders, kneaders, double planetarymixers, triple planetary mixers, high pressure homogenizers, ball mills,attrition equipment, sandmills, horizontal and vertical wet grindingmills, etc. Processing (including grinding) technologies can be wet ordry and can be continuous or discontinuous. Suitable materials for useas grinding media include metals, carbon steel, stainless steel,ceramics, stabilized ceramic media (such as yttrium stabilized zirconiumoxide), PTFE, glass, tungsten carbide, etc. Methods such as these can beused to change the particle size and/or morphology of the graphite,graphene sheets, other components, and blends or two or more components.

Components may be processed together or separately and may go throughmultiple processing (including mixing/blending) stages, each involvingone or more components (including blends).

There is no particular limitation to the way in which the graphenesheets, graphite (if used), and other components are processed andcombined. For example, graphene sheets and/or graphite may be processedinto given particle size distributions and/or morphologies separatelyand then combined for further processing with or without the presence ofadditional components. Unprocessed graphene sheets and/or graphite maybe combined with processed graphene sheets and/or graphite and furtherprocessed with or without the presence of additional components.Processed and/or unprocessed graphene sheets and/or processed and/orunprocessed graphite may be combined with other components, such as oneor more binders and then combined with processed and/or unprocessedgraphene sheets and/or processed and/or unprocessed graphite. Two ormore combinations of processed and/or unprocessed graphene sheets and/orprocessed and/or unprocessed graphite that have been combined with othercomponents may be further combined or processed.

In one embodiment, if a multi-chain lipid is used, it is added tographene sheets (and/or graphite if present) before processing.

After blending and/or grinding steps, additional components may be addedto the compositions, including, but not limited to, thickeners,viscosity modifiers, binders, etc. The compositions may also be dilutedby the addition of more carrier.

The compositions may optionally comprise one or more additionaladditives, such as dispersion aids (including surfactants, emulsifiers,and wetting aids), adhesion promoters, thickening agents (includingclays), defoamers and antifoamers, biocides, additional fillers, flowenhancers, stabilizers, crosslinking and curing agents, etc.

Examples of dispersing aids include glycol ethers (such as poly(ethyleneoxide), block copolymers derived from ethylene oxide and propylene oxide(such as those sold under the trade name Pluronic® by BASF), acetylenicdiols (such as 2,5,8,11-tetramethyl-6-dodecyn-5,8-diol ethoxylate andothers sold by Air Products under the trade names Surfynol® and Dynol®),salts of carboxylic acids (including alkali metal and ammonium salts),and polysiloxanes.

Examples of grinding aids include stearates (such as Al, Ca, Mg, and Znstearates) and acetylenic diols (such as those sold by Air Productsunder the trade names Surfynol® and Dynol®).

Examples of adhesion promoters include titanium chelates and othertitanium compounds such as titanium phosphate complexes (including butyltitanium phosphate), titanate esters, diisopropoxy titaniumbis(ethyl-3-oxobutanoate, isopropoxy titanium acetylacetonate, andothers sold by Johnson-Matthey Catalysts under the trade name Vertec.

Examples of thickening agents include glycol ethers (such aspoly(ethylene oxide), block copolymers derived from ethylene oxide andpropylene oxide (such as those sold under the trade name Pluronic® byBASF), long-chain carboxylate salts (such aluminum, calcium, zinc, etc.salts of stearates, oleats, palmitates, etc.), aluminosilicates (such asthose sold under the Minex® name by Unimin Specialty Minerals andAerosil® 9200 by Evonik Degussa), fumed silica, natural and syntheticzeolites, etc.

The compositions may optionally comprise at least one “multi-chainlipid”, by which term is meant a naturally-occurring or synthetic lipidhaving a polar head group and at least two nonpolar tail groupsconnected thereto. Examples of polar head groups include oxygen-,sulfur-, and halogen-containing, phosphates, amides, ammonium groups,amino acids (including α-amino acids), saccharides, polysaccharides,esters (Including glyceryl esters), zwitterionic groups, etc.

The tail groups may be the same or different. Examples of tail groupsinclude alkanes, alkenes, alkynes, aromatic compounds, etc. They may behydrocarbons, functionalized hydrocarbons, etc. The tail groups may besaturated or unsaturated. They may be linear or branched. The tailgroups may be derived from fatty acids, such as oleic acid, palmiticacid, stearic acid, arachidic acid, erucic acid, arachadonic acid,linoleic acid, linolenic acid, oleic acid, etc.

Examples of multi-chain lipids include, but are not limited to, lecithinand other phospholipids (such as phosphoglycerides (includingphosphatidylserine, phosphatidylinositol, phosphatidylethanolamine(cephalin), and phosphatidylglycerol) and sphingomyelin); glycolipids(such as glucosyl-cerebroside); saccharolipids; sphingolipids (such asceramides, di- and triglycerides, phosphosphingolipids, andglycosphingolipids); etc. They may be amphoteric, includingzwitterionic.

The compositions may optionally comprise one or more charged organiccompounds. The charged organic compound comprises at least one ionicfunctional group and one hydrocarbon-based chain. Examples of ionicfunctional groups include ammonium salts, sulfates, sulphonates,phosphates, carboxylates, etc. If two or more ionic functional groupsare present, they may be of the same or different types. The compoundmay comprise additional functional groups, including, but not limited tohydroxyls, alkenes, alkynes, carbonyl groups (such as carboxylic acids,esters, amides, ketones, aldehydes, anhydrides, thiol, etc.), ethers,fluoro, chloro, bromo, iodo, nitriles, nitrogen containing groups,phosphorous containing groups, silicon containing groups, etc.

The compound comprises at least one hydrocarbon-based chain. Thehydrocarbon-based chain may be saturated or unsaturated and may bebranched or linear. It may be an alkyl group, alkenyl group, alkynylgroup, etc. It need not contain only carbon and hydrogen atoms. It maybe substituted with other functional groups (such as those mentionedabove). Other functional groups, such as esters, ethers, amides, may bepresent in the length of the chain. In other words, the chain maycontain two or more hydrocarbon-based segments that are connected by oneor more functional groups. In one embodiment, at least one ionicfunctional group is located at the end of a chain.

Examples of ammonium salts include materials having the formula:R¹R²R³R⁴N⁺X⁻, where R¹, R², and R³, are each independently H, ahydrocarbon-based chain, an aryl-containing group, an alicyclic group;an oligomeric group, a polymeric group, etc.; where R⁴ is ahydrocarbon-based chain having at least four carbon atoms; and where X⁻is an anion such as fluoride, bromide, chloride, iodide, sulfate,hydroxide, carboxylate, etc. Any of the R groups may have one or moreadditional ammonium groups.

Examples of R groups include methyl, ethyl, propyl, butyl, pentyl,hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl,tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl,eicosyl, C₂₁ to C₄₀ chains, etc.

Examples of quaternary ammonium salts include tetraalkylammonium salts,dialkyldimethylammonium salts, alkyltrimethylammonium salts, where thealkyl groups are one or more groups containing at least eight carbonatoms. Examples include tetradodecylammonium,tetradecyltrimethylammonium halide, hexadecyltrimethylammonium halide,didodecyldimethylammonium halide, etc.

Ammonium salts may be bis- or higher order ammonium salts, includingquaternary ammonium salts. They may be salts of carboxylic acids,dicarboxylic acids, tricarboxylic acids, and higher carboxylic acids.The carboxylic acids may have be part of a hydrocarbon-based chainhaving at least about four linear carbon atoms. Examples includeammonium salts of octanoic acid, nonanoic acid, decanoic acid,undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid,pentadecanic acid, carboxylic acids having at least 15 carbon atoms,stearic acid, oleic acid, montanic acid, apidic acid, 1,7-heptanedioicacid, 1,8-octandioic acid, 1,9-nonanedioic acid, sebacic acid,1,11-undecandioic acid, 1,12-dodecanedioic acid, 1,13-tridecanedioicacid, 1,14-tetradecanedioic acid, 1,15-pentadecanedioic acid,1,16-hexadecanedioic acid, 1,17-heptadecanedioic acid,1,18-octadecanedioic acid, 1,19-nonadecanedioic acid, 1,20-eicosanedioicacid, dicarboxylic acids having 21 to 40 carbon atoms, etc.

Alkylol ammonium salts of carboxylic acids (including high molecularweight carboxylic acids and unsaturated carboxylic acids) may be used.Examples include EFKA 5071, an alkylol ammonium salt of a high-molecularweight carboxylic acid supplied by Ciba and BYK-ES80, an alkylolammoniumsalt of an unsaturated acidic carboxylic acid ester manufactured by BYKUSA, Wallingford, Conn.

The charged organic compound may have a sulfur containing group such asa sulphonate, mesylate, triflate, tosylate, besylate, sulfates, sulfite,peroxomonosulfate, peroxodisulfate, pyrosulfate, dithionate,metabisulfite, dithionite, thiosulfate, tetrathionate, etc. The organiccompound may also contain two or more sulfur containing groups.

Alkyl, alkenyl, and/or alkynyl sulfates and sulphonates are preferredsulfur-containing compounds. The alkyl, alkenyl, and/or alkynyl groupspreferably contain at least about 8 carbon atoms, or more preferably atleast about 10 carbon atoms. Examples include decylsulfate salts,dodecylsulfate salts (such as sodium 1-dodecanesulfate (SDS)),decylsulfonate salts, dodecylsulfonate salts (such as sodium1-dodecanesulfonate (SDSO)), etc. The counter ions may be any suitablecation, such as lithium, sodium, potassium, ammonium, etc.

The charged organic compound may be present in about 1 to about 75weight percent, in about 2 to about 70 weight percent, in about 2 toabout 60 weight percent, in about 2 to about 50 weight percent, in about5 to about 50 weight percent, in about 10 to about 50 weight percent, inabout 10 to about 40 weight percent, in about 20 to about 40 weightpercent, based on the total weight of charged organic compound andgraphene sheets and other carbonaceous fillers, if used.

The coating compositions may optionally contain additional electricallyconductive components other than the graphene sheets, such as metals(including metal alloys), conductive metal oxides, polymers,carbonaceous materials other than compositions, metal-coated materials,etc. These components can take a variety of forms, including particles,powders, flakes, foils, needles, etc.

Examples of metals include, but are not limited to silver, copper,aluminum, platinum, palladium, nickel, chromium, gold, bronze, colloidalmetals, etc. Examples of metal oxides include antimony tin oxide andindium tin oxide and materials such as fillers coated with metal oxides.Metal and metal-oxide coated materials include, but are not limited tometal coated carbon and graphite fibers, metal coated glass fibers,metal coated glass beads, metal coated ceramic materials (such asbeads), etc. These materials can be coated with a variety of metals,including nickel.

Examples of electrically conductive polymers include, but are notlimited to, polyacetylene, polyethylene dioxythiophene (PEDOT),poly(styrenesulfonate) (PSS), PEDOT:PSS copolymers, polythiophene andpolythiophenes, poly(3-alkylthiophenes),poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT),poly(phenylenevinylene), polypyrene, polycarbazole, polyazulene,polyazepine, polyflurorenes, polynaphthalene, polyisonaphthalene,polyaniline, polypyrrole, poly(phenylene sulfide), copolymers of one ormore of the foregoing, etc., and their derivatives and copolymers. Theconductive polymers may be doped or undoped. They may be doped withboron, phosphorous, iodine, etc.

Examples of carbonaceous materials other than graphene sheets andgraphite include, but are not limited to, graphitized carbon, carbonblack, carbon fibers and fibrils, carbon whiskers, vapor-grown carbonnanofibers, metal coated carbon fibers, carbon nanotubes (includingsingle- and multi-walled nanotubes), fullerenes, activated carbon,carbon fibers, expanded graphite, expandable graphite, graphite oxide,hollow carbon spheres, carbon foams, etc.

After they have been applied to the patterned substrate, if necessary,the coating compositions may be cured using any suitable technique,including drying and oven-drying (in air or another inert or reactiveatmosphere), UV curing, IR curing, drying, crosslinking (including freeradical crosslinking, electron beam crosslinking, etc.), thermal curing,laser curing, microwave curing or drying, sintering, and the like toform the electrode.

In some embodiments, the curing may be thermal curing and may take placeat a temperature of no more than about 135° C., or no more than about120° C., or no more than about 110° C., or no more than about 100° C.,or no more than about 90° C., or no more than about 80° C., or no morethan about 70° C.

The coated patterns can have conductivities of at least about 10⁻⁸ S/m.They can have a conductivities of about 10⁻⁶ S/m to about 10⁵ S/m, or ofabout 10⁻⁵ S/m to about 10⁵ S/m. In other embodiments of the invention,the electrodes have conductivities of at least about 0.001 S/m, of atleast about 0.01 S/m, of at least about 0.1 S/m, of at least about 1S/m, of at least about 10 S/m, of at least about 100 S/m, or at leastabout 1000 S/m, or at least about 10,000 S/m, or at least about 20,000S/m, or at least about 30,000 S/m, or at least about 40,000 S/m, or atleast about 50,000 S/m, or at least about 60,000 S/m, or at least about75,000 S/m, or at least about 10⁵ S/m, or at least about 10⁶ S/m.

In some embodiments, the surface resistivities of the coated patternsmay be no greater than about 500 Ω/square, or no greater than about 350Ω/square, or no greater than about 200 Ω/square, or no greater thanabout 200 Ω/square, or no greater than about 150 Ω/square, or no greaterthan about 100 Ω/square, or no greater than about 75 Ω/square, or nogreater than about 50 Ω/square, or no greater than about 30 Ω/square, orno greater than about 20 Ω/square, or no greater than about 10 Ω/square,or no greater than about 5 Ω/square, or no greater than about 1Ω/square, or no greater than about 0.1 Ω/square, or no greater thanabout 0.01 Ω/square, or no greater than about 0.001 Ω/square.Conductivities and surface resistivities are typically measured afterthe coatings have been cured.

In some embodiments, the coated patterns can have a thermal conductivityof about 0.1 to about 50 W/(m-K), or of about 0.5 to about 30 W/(m-K),or of about 1 to about 30 W/(m-K), or of about 1 to about 20 W/(m-K), orof about 1 to about 10 W/(m-K), or of about 1 to about 5 W/(m-K), or ofabout 2 to about 25 W/(m-K), or of about 5 to about 25 W/(m-K).

The coating compositions may be applied to the patterned substrate usingany suitable method, including those described above for the applicationof the pattern to the substrate.

The security devices may be incorporated into larger structures ordevices. Not all of the substrate need be coated and other areas of thesubstrate may have other functionality. They may be connected toelectrical or electronic circuits or other electrical or electroniccomponents. They may be used in anti-fraud, anti-tampering,anti-counterfeiting, anti-theft, tracking, forensics, authentication(including product authentication), inventory control, etc.applications.

The security devices may be used in financial applications, such aschecks, money orders, banknotes, stock certificates, bearer bonds, andother instruments. They may be used in passports, drivers' licenses, andidentification cards, social security cards, motor vehicleregistrations, postage stamps, tax stamps, security paper, certificatesof authenticity, legal documents, vital records certificates (e.g.,birth, death, marriage, etc. records), automobile and land titles,permits, election documents, health records, transcripts, prescriptionforms, parking and mass transit passes and permits, secure letterhead,warranties and guarantees, coupons and rebates, bills of lading andother shipping documents, etc. They may be used for lottery tickets,game cards, gift cards, gift certificates, scratch-off cards, loyaltycards, phone cards, credit/debit cards, smart cards, event tickets, etc.They may be used to make documents that when copied do not contain thedistinctive features of the security devices.

The security devices may contain barcode (including two- andthree-dimensional barcode) information. They may contain identificationinformation.

The security devices may be used in packaging, including pharmaceuticaland food-related packaging applications and applications wheretamper-resistant and tamper-evident packaging is needed. They may beused to secure shipments, etc. They may be used with valuables such asart, collectibles, electronics, designer goods, etc. They may be usedfor brand protection.

The devices may be designed to be covert and undetectable to theinitiated, making tampering very difficult. They may offer two or morelayers of security (such as through electrical conductivity, thermalconductivity, optical density, color coordinates, XRD patterns,variations in properties in different regions of the coated pattern,etc.). By varying how the pattern is applied to the substrate and/or howthe coating is applied to the pattern, each copy of a particular item tobe secured could be given a device having a signature unique to thatparticular copy.

EXAMPLES

Six blocks, corresponding to about 5, 20, 40, 60, 80, and 100% gray areprinting using a laser printer onto plain printer paper. The six blocksand unimaged portions of the paper sheet are overcoated with a coatingcomprising graphene sheets, graphite, an acrylate binder, and solventusing a #28 wire rod. The coated paper is dried at about 125° C. forabout 4 minutes. The surface resistivities of each block as wellportions of the paper that were not printed with toner (indicated as 0%gray) are measured using a four-point probe. The results are given inTable 1.

TABLE 1 Surface resistivity % Gray (Ohm/sq) 0 20 5 26 20 30 40 42 60 5780 60 100 67

The invention claimed is:
 1. A combination comprising: a document havingan image applied thereto; a security device affixed to a surface of thedocument and comprising: a first layer applied to the image, the layercomprising a first portion and a second portion in communication with afirst image area of the image and a second image area of the image,respectively; and the first layer comprising a coating compositioncomprising fully exfoliated single sheets of graphene; and wherein thefirst portion comprises a first detectable property comprising: a firstvalue correlated with the fully exfoliated single sheets of graphene;and a first X-ray diffraction pattern and a first electricalconductivity; the second portion comprises a second detectable propertycomprising: a second value correlated with the fully exfoliated singlesheets of graphene; and a second X-ray diffraction pattern and a secondelectrical conductivity; the first detectable property and the seconddetectable property are not equal; and together create a distinctivesignature; and an electrical or electronic component conductivelycoupled to the security device.
 2. The combination of claim 1, whereinthe coating composition further comprises a polymer binder comprisingone or more of an acrylate polymer, an epoxy, a polyamide, poly(vinylbutryal), poly(vinyl pyrrolidone), poly(vinyl acetate), a vinyl acetateand vinyl pyrrolindone copolymer, poly(lactic acid), cellulosic polymer,a polycarbonate, a polyolefin, and a polysiloxane.
 3. The combination ofclaim 1, wherein the coating composition further comprising amulti-chain lipid.
 4. The combination of claim 1, wherein some or all ofthe image is visible through the coating composition.
 5. The combinationof claim 1, wherein the security device is included in a tamper-evidentpackaging.
 6. A method to fabricate a combination, comprising:exfoliating graphite to thereby form fully exfoliated single sheets ofgraphene; preparing a coating composition comprising fully exfoliatedsingle sheets of graphene; applying the coating composition to a firstimage area and a second image area of an image on a document,respectively; and further forming a conductive coupling between thesecurity device and one or an electrical or electronic component, of animage on a document thereby forming a security device having a firstportion and a second portion, respectively; wherein the first portioncomprises a first detectable property comprising a first valuecorrelated with the fully exfoliated single sheets of graphene; thesecond portion comprises a second detectable property comprising asecond value correlated with the fully exfoliated single sheets ofgraphene; the first detectable property is not equal to the seconddetectable property; the first detectable property comprises a firstX-ray diffraction pattern and a first electrical conductivity; thesecond detectable property comprises a second X-ray diffraction patternand a second electrical conductivity; and the first detectable propertyand the second detectable property together create a distinctivesignature.
 7. The method of claim 6, wherein preparing the coatingcomposition comprises combing the fully exfoliated single sheets ofgraphene with a polymer binder.
 8. The method of claim 7, wherein thepolymer binder comprises one or more of an acrylate polymer, an epoxy, apolyamide, poly(vinyl butryal), poly(vinyl pyrrolidone), poly(vinylacetate), a vinyl acetate and vinyl pyrrolindone copolymer, poly(lacticacid), cellulosic polymer, a polycarbonate, a polyolefin, and apolysiloxane.
 9. The method of claim 6, wherein preparing the coatingcomposition comprises combining the fully exfoliated single sheets ofgraphene with a multi-chain lipid.
 10. The method of claim 6, whereinapplying the coating composition to the first image area and the secondimage area of the image comprises allowing some or all of the image tobe visible through the applied coating composition.